Join Brian Bradley for an in-depth discussion in this video Using the DMC Sampler, part of V-Ray 2.0 for Maya Essential Training.
To produce what are termed, in rendering parlance, as blurry, or noisy render effects, internally, the V-Ray render engine makes extensive use of a class of randomized computational algorithms known as deterministic Monte Carlo, or DMC algorithms, as we will refer to them. This means that wherever V-Ray is working on effects such as those shown in our slide -- so image sampling, depth of field, indirect illumination, area shadows, blurry reflections and refractions, translucency, motion blur, and many others -- well, in these instances, DMC algorithms are being utilized.
As you might guess, because DMC algorithms are so heavily involved in V-Ray's rendering process, getting our DMC sampler settings wrong can cause lots of problems when it comes to the speed and quality of our renders. To show you where the controls are, we want to come up to our Render Settings icon. If we just click on that that, we will bring up the Render Settings dialog, and if we come along to our Settings tab, you can see the very top rollout -- the initial rollout -- houses our DMC sampler controls. An in depth discussion of what the DMC algorithms and the sampler controls themselves are doing behind the scenes really does fall outside of the scope of this essentials training course, but what we thought would prove useful would be to just take a minute or two to suggest, and demonstrate to you some good general usage values that can potentially help us with our renders in terms of both their speed and final quality.
Of course, once we've familiarized ourselves completely with using the V-Ray render engine, we will be able to tweak our DMC Sampler settings on a per render basis. That way, we'll really get the best out of each V-Ray rendering session. Just so that you're aware, the settings we will work with in this video are assuming you have not adopted what is known in V-Ray rendering circles as the universal settings approach. These values would not fit into that particular workflow. Now, before we go ahead I make some changes to our DMC Sampler controls, we just want to make a couple of tweaks to our scene, so that your final renders will match the pre-rendered images we are working with here.
We are just going to drop the light values down a little bit, so that we don't get too much of this blowout, because once we are able to see where our noise is falling in the scene. If you want to work with the pre-rendered images that we are viewing here, you can do so. If we just come to File, come to Open Image, and if we just come up a little bit, you can see we are inside our Exercise_Files folder. If you come into the assets folder, you'll see there are number of chapters in here; all listed. Each of these have rendered images; they have assets in there that you can take a look at, and work along with different aspects of this course if you want to.
In this case, we're working, of course, in Chapter 02, and inside the DMC folder, and these are the images that we're going to be viewing in just a moment. So you're aware that all of those files are there. If we just come into the V-Ray tab, I want you to come into the Image sampling controls, and we're just going to change our maximum subdivision setting from a value of 2 up to 16. This will just give us a little bit more leeway in terms of the samples that are available to V-Ray for rendering. We also want to come up to the Window menu, come down to Outliner, and if you just select the first of our V-Ray rectangular lights listed there, and we can come into the Attributes Editor; we just want to drop the multiplier value down from a value of 30 to 20, and as we said, that will just give us a little bit less blowout in our renders.
So, now we can come back to our Render Settings dialog, and of course, back into our DMC Sampler controls. In terms of general rendering, we can pretty much leave everything in here set at it its default, and just work with this adaptive threshold value. Using this value, we can quickly switch between what we could think of as draft and final render settings. Threshold values between 0.1 and 0.01 are good for preview or test renders. These values will very rarely make V-Ray work too hard to clean up our images; it won't use too many of those 16 subdivisions in the image sampling settings.
So let's just take a look at the kind of renders we would get. So let's just set this to a value of 0.1, and if we took a render with the scene, we would get this particular render back, which as you can see, has a lots of feedback in it. We can tell what I am lighting, what our global illumination is doing, but in terms of the noise in the scene, well, that may get in the way of working with attributes, such as materials, that we may want to be testing in our renders. To do that, we would obviously need to clean things up a little bit. So let's come and set our DMC Sampler controls to 0.01, and now we would go from this, to this, which as we can see, is considerably cleaner.
Of course, we have increased our render times quite a bit, but now we've got a much cleaner scene, and we could definitely work with materials and such inside of our renders. If we wanted to push on to final production render quality, though, maybe we would need to just make our DMC Sampler controls a little more sensitive; make them work a little bit harder to clean up the noise in the scene. So a value 0.007 can often times work very nicely, or something around there. Obviously, these are suggesting, here, a range of values that can work; you don't have to use the exact numerical values.
But now we would go from this, to this, which as you can see, has just cleaned up the noise a little bit more. If we just quickly flick backwards, and forwards, you can see there is a little bit of cleanup. If we had materials, surface materials here, that had bump mapping, or blurry reflections, oftentimes, this level of noise can get lost into that mix, so we could get away with this as a final production setting, and of course, we would still be getting fairly reasonable render times back. If, however, we really needed to clean up our scene -- if we wanted to make our DMC Sampler controls, and our Image sampling settings really work to eliminate noise in the scene -- let's see what we would get if we go all the way down to a value of 0.002.
Now we would see that we have a pretty noiseless scene. We can take a look at our very soft area shadows here, and we can see that they are very, very smooth indeed. Now, if we are rendering animated sequences, this Time Dependent checkbox will be important to us. Left unchecked, noise patterns from frame to frame would be identical, which of course, in an animated sequence, can oftentimes be undesirable, as static noise will draw attention to itself. To have the sampling patterns change a little over time, all we need to do is put a check in that Time Dependent checkbox, and that will work nicely for us.
So, hopefully, as you can see, the DMC Sampler does play a critical role in the V-Ray rendering process, and yet oftentimes, it gets ignored by users, or maybe just tweaked a little bit as an afterthought. We've included this video in this portion of our course to hopefully help you avoid making just such a mistake. When working with V-Ray's quality control settings, we need to make certain that the DMC Sampler controls are properly set. We are using values that are going to work according to the quality requirements of our particular scene.
- Installing and setting up V-Ray
- Using the DMC Sampler
- Understanding color mapping modes
- Adding a spherical fill light
- Working with the V-Ray Dome Light
- Using irradiance mapping and the Light cache
- Creating diffuse color
- Making reflective materials
- Creating translucency
- Ensuring quality with image sampling
- Controlling the V-Ray physical camera
- Creating a motion blur effect
- Compositing V-Ray elements